1. Field of the Inventions
Embodiments of the present invention generally relate to the transportation of large fluid volumes in a vessel. More particularly, embodiments of the present invention relate to tank designs for the reduction of loads due to sloshing of contained fluids, such as liquefied natural gas.
2. Description of Related Art
The transportation of liquefied natural gas (or “LNG”) through marine bodies is oftentimes accomplished by storing LNG at very low temperatures within membrane tanks. In one form, membrane tanks are prismatic in shape, meaning that that they are shaped to generally follow the contours of the ship's hull. The tank will typically consist of insulating panel membranes joined to the inside of a smooth-walled steel tank hold. The hull provides reinforcement to the membrane tank, thereby strengthening the tank against hydrostatic and dynamic forces generated by the contents.
Membrane containment structures are generally constructed of either stainless steel or Invar. Invar is a high nickel content alloy having minimal thermal expansion characteristics. Both a primary and a secondary containment barrier are typically provided. Insulation panels are then placed between the primary and secondary barriers. The insulation panels are usually made from either blocks of plywood-reinforced polyurethane foam, or stiffened plywood boxes containing perlite as insulation.
It is desirable to increase the size of LNG carriers so that fewer ships are required to transport equivalent volumes of gas. Larger ships allow for larger tanks and larger corresponding containment volumes. However, larger volumes may induce higher “sloshing” loads within the membrane's primary and secondary barriers. This potential exists even at high fill levels.